You get one pedal. What is it?

If you could only use one pedal (tuner doesn't count for this hypothetical), what is it? I've vacillated between different pedalboards and have settled for now on just using guitar-distortion pedal-amp (Big Muff or Crunch Box depending on the mood). Having done such, it inspired me to ask here, what's the one pedal you would use if you had to strip down your setup? Modulation and distortion count as the same, you have to pick only one pedal. Amp modulation is okay (reverb, tremolo, etc.)

For this exercise, I choose the Crunch Box. It gives me a wide palette of gain stages and its voicing is exactly what I want for distortion, amp or pedal. My playing style also doesn't require any effects, so distortion is a bonus.

I've thought about this recently. If ideally I had and amp with verb & trem and could run it dirty and use guitar volume knob for clean>dirt tones, all I would really "need" in addition would be a delay.

So I would have a quality delay with LOTS of options (even a small looper), would run the amp at 7-8 and turn down the volume at 3-4 for clean. The only POSSIBLE setup I could go with. I can also run the tremolo and reverb straight from the amp!